Ford is dismissing the need to recall its Ford Explorer SUV despite a growing number of drivers who have reported incidents of dizziness, nausea and vomiting to federal regulators, who are conducting an active investigation into the complaints.

The National Highway Traffic Safety Administration confirmed Tuesday its investigation into Ford Explorer model years 2011 to 2017 is ongoing after a consumer safety group repeated its appeal for a recall.

The issue has extended to the Explorers modified for police use. Ford said it hasn't found any problems or carbon monoxide intrusion into the vehicles' cabins that could explain the problem.

"Explorers are safe," said Elizabeth Weingandt, safety communications manager. "Ford’s investigation and extensive testing has not found carbon monoxide levels that exceed what people are exposed to every day."

She said customers can bring their vehicle to their local Ford dealer for a free service designed to reduce their concern.

NHTSA officials, however, say Ford's customer satisfaction campaign does not bring closure to this issue.

More than 1,300 Ford Explorer owners have reported issues to the federal safety officials, who began investigating in 2016.

On Tuesday, the non-profit Center for Auto Safety sent a letter to Ford CEO Jim Hackett renewing an October 2017 request for the Dearborn, Mich.-based company to recall 1.33 million Explorers from model years 2011 to 2017 for suspected carbon monoxide leaks.

Ford Explorer-based Police Interceptors sit in a police station parking in Chicago. Police departments are beginning to take the SUVs out of service because the say fumes from the exhaust system are seeping into the SUVs passenger compartment and making officers sick.(Photo: Scott Olson, Getty Images)

In July 2017, federal transportation officials expanded their probe into reports of exhaust odors in vehicle compartments and exposure to carbon monoxide that may be linked to crashes and injuries. The oversight agency said at the time it was aware of the growing complaints and crashes that may have been linked to exposure to carbon monoxide and dozens of injuries among police and civilian vehicles.

Ford has issued multiple technical service bulletins related to exhaust odor to address complaints from police fleets and other owners, the federal agency noted. And Ford has said a dedicated team was working to investigate and resolve issues.

The federal investigation is now in "engineering analysis" status, a step before the agency can formally demand an automaker conduct a recall if it believes vehicles pose an unreasonable risk to safety.

The agency obtained preliminary testing that suggests carbon monoxide levels may be elevated in certain driving scenarios, “although the significance and effect of those levels remains under evaluation,” according to 2017 reports.

“Unfortunately, the only thing that triggers action is tragedy,” said Jason Levine, executive director of the Center for Auto Safety. “We’re hoping to see action taken by America’s leading auto brand before something awful happens. Unless we’re going to wait until there’s a report of someone crashing and dying, there’s no time like the present.”

On Jan. 12, 2018, a White Plains, N.Y., father filed a complaint with federal officials reporting his 2017 Ford Explorer had exhaust fumes in the cabin that left his wife with severe headaches after 60 minutes of driving with their 20-month-old baby.

“My car has already been repaired once and is in the shop again. ... Ford is not being very helpful because I don’t want the car anymore. It is a huge safety concern and I don’t want my wife and toddler in the vehicle at all,” he wrote in the filing.

A 70-year-old from Manistee, Mich., wrote of becoming "deathly ill" while driving and having to pull over and call an ambulance. Symptoms matched carbon monoxide poisoning. Later, the driver reported getting dizzy and disoriented and nearly passing out. The Explorer owner bikes 20 miles a day two to three days a week, plays league hockey and golf.

Steve Simmons, 63, a retired IBM worldwide marketing project manager from Raleigh, N.C., bought his 2015 Explorer certified from a Ford dealership. He purchased his Explorer in July and started having headaches, weakness, dizziness and blurred vision, his report to NHTSA said. After his doctor sent him to Duke Raleigh Hospital, a blood test confirmed elevated carbon monoxide levels.

“An Explorer recall is necessary. There’s abundant evidence. Sending technical support bulletins and customer service letters doesn’t get the job done,” he said Tuesday. “I’ve never smoked a cigarette in my life. I have hard-wired carbon monoxide detectors in my house. I swim a mile in the pool three to four times a week. I do volunteer construction. I teach high-adventure sports to kids. I had that Ford Explorer 16 days. When I got out of the hospital I went to the dealership and told them that vehicle nearly killed me.”

The dealership swapped it for a 2015 Ford F-150. “But I’m irritated how Ford has treated other people. If we're not organized, they can afford to ignore you and pretend you don’t exist.”

Ford has acknowledged a carbon monoxide issue with vehicles sold for police use. The company determined issues were caused by after-market modification handled outside Ford. Lawsuits have been filed by law enforcement officers.

Donna Talbot, 57, of Lafayette, La., said Tuesday she and her husband — both former truck drivers who loved their old Ford Explorer — are angry and embarrassed.

“We feel so stupid,” she said. “We did not expect carbon monoxide poisoning from a brand new vehicle.”

They bought their 2015 Explorer on a Wednesday and returned it to the dealership within 48 hours, she said. After a series of trips back and forth, the Explorer sits in their carport with 10,000 miles on it. A trip to Dallas left the family sick with headaches and vomiting. Talbot will only drive her 1999 Explorer with 187,000 miles.

“We’ve been fighting this for three years,” she said. “We put $25,000 cash down and with insurance pay $500 month now. We can’t even use it. We drove around with a carbon monoxide detector and it just jumps up the faster you go. I don’t know how Ford can say these levels are safe.”

Carbon monoxide is responsible for more than 400 unintentional deaths annually in the U.S., according to the Centers for Disease Control and Prevention.

The Ford Explorer owner’s manual contains the warning, “Do not drive your vehicle if you smell exhaust fumes. Carbon monoxide is present in exhaust fumes. Take precautions to avoid its dangerous effects.”

Numerous reports filed with the Department of Transportation agency describe the smell of exhaust fumes in Explorers, which are assembled at the company's Chicago Assembly Plant.

In July 2017, NHTSA indicated the most likely culprit for the exposure was cracked exhaust manifolds, Levine noted.

“Ford needs to stop sending mixed messages to Explorer owners and passengers, including senior citizens and parents of young children, that the vehicles are ‘safe’ and that repairs are available only for ‘peace of mind,' " Levine said. "Since some Ford dealers are responsibly replacing cracked exhaust manifolds, it is time for Ford to take a more serious step, recall all of these vehicles and inspect and replace cracked exhaust manifolds.”

He said the 48-year-old consumer advocacy group has been contacted by families in Maryland, California, Iowa and Louisiana seeking help. They report grandchildren vomiting, children losing consciousness and ending up in the emergency room after calling 911, even seizures.

“Carbon monoxide should be taken seriously," said Paul Billings, a national senior vice president at the American Lung Association. "Individuals should take steps to prevent exposure to high levels of carbon monoxide because of the serious health consequences that can result, including death.”

Federal safety officials said they will continue to evaluate complaints submitted to the agency and will review the completion rate of vehicles repaired under Ford's customer service program. Federal officials encourage owners to contact dealers. The agency asked that owners who experience exhaust odor or have concerns about carbon monoxide exposure contact NHTSA by calling 888-327-4236 or going to NHTSA.gov and clicking "report a problem."